Although regulation of receptor activity is abnormal in many neurologic and metabolic diseases, we do not understand the biochemical mechanisms which regulate receptor function in the post-synaptic membrane. We have discovered that the membrane-bound acetylcholine receptor (AChR) is reversibly phosphorylated and dephosphorylated in situ by a membrane protein kinase and phosphatase. Such a reversible covalent biochemical modification of a neuroreceptor is likely to be of fundamental importance in the pathophysiology of many disorders of receptor function. The specific aims in this proposal are to characterize the regulation of AChR phosphorylation in receptor-enriched membrames, investigate the relation of receptor phosphorylation to receptor function (e.g. desensitization), determine whether the mammalian AChR is phosphorylated and investigate the relation of phosphorylation to receptor maintenance and localization in the post-synaptic membrane. We will use sealed right-side out receptor-enriched vesicles, autoradiographic and immunoprecipitation techniques, radiochemical assays for membrane protein kinase and phosphatase activities and ion fluxes, chemical electrodes to measure ion permeability and changes in membrane potential, and radioligand receptor binding assays. Our long term objective is to understand the molecular mechanisms which regulate receptor-mediated events and which are abnormal in disorders of receptor function.